//px转换rem /10

(function(doc, win) {  
 var docEl = doc.documentElement,  
 resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',  
 recalc = function() {  
 var clientWidth = docEl.clientWidth;
 if (!clientWidth) return;  
 docEl.style.fontSize = 20 * (clientWidth / 750) + 'px';  
 };  
   if (!doc.addEventListener) return;  
 win.addEventListener(resizeEvt, recalc, false);  
 doc.addEventListener('DOMContentLoaded', recalc, false);  
 })(document, window);  